Hi Jon, Richard, Ray, folks,
I've been looking though the DNS-applications draft, and I'm unsure on its
We've already discussed the potential for "ENUM-Ops" style work to put
on how ENUM and ENUM-like systems should be used. The fact that there has been
on the appropriate mailing lists on that topic doesn't mean that task has been
(there have been other distractions :).
There is certainly a good reason to issue DNS application guidance now,
and some of the features of DNS may not be what applications expect.
... BUT ...
Q: Are you arguing that some applications will make cacheing less effective and
that this will be a problem?
Q: Are you arguing that over-use of DNS is generally a problem (e.g. due to
lack of prioritisation of query processing)?
Q: Are you arguing that volume and size of data will unbalance intermediary
cacheing servers and undermine their effectiveness/"hit rate"?
Q: Are you arguing that the size of RRSets will cause upstream servers to face
difficult decisions in populating the answer and authority section of DNS
Q: Are you arguing that the size of RRSets will force difficult decisions on
upstream servers populating the additional section of DNS responses?
Q: Are you concerned that answers may vary depending on who's asking, and that
this may damage the effectiveness of cacheing and/or the DNS infrastructure?
-- consider the Yahoo/Google (edns-client-subnet) proposals for
Internet-answering resolvers to support CDNs better (dwarfing use in
private/internal telecommunications data networks)
-- consider the Google opt-in scheme for IPv6 networks, giving different
answers depending on whether or not the network is "known to work with" IPv6
+: see <http://www.google.com/intl/en/ipv6/> for requirements
I believe that there ARE underlying issues with application use of DNS, and so
guidance is definitely needed.
I'm however not convinced that the current draft chooses the best exemplars of
* Frankly, the dynamism of the telecommunications data set is low (as you all
The queries are susceptible to cacheing (or the systems WILL be designed to
cope, where that is not a valid assumption).
(ASSUMING OF COURSE THAT "in-use" STATUS IS NOT TO BE REFLECTED IN DNS. No-one
has ever suggested to me that fine grained presence data should be in DNS, yet
that seems to be the only valid coherency concern).
* Telecommunications data is under the control of those provisioning the data
For Telecommunication data provisioning, synchronisation seems to be an issue
only of appropriate TTLs.
Dynamic update DNS services already face this issue and deal with it.
- "Applications should consider data dynamism and DNS synchronisation" is an
eminently valid guideline, but ISPs' dynamic address assignment and third party
Dynamic DNS services would seem a more appropriate example.
* The size of ENUM answers is subject to the same restrictions as other users
Performance may will be helped by support for EDNS, but this is needed for all
users of DNSSEC.
The approach used already (for example) for gmail.com's MX records has NOT been
proposed for public ENUM use.
It's unclear if the concern over size raised in the DNS-applications draft will
be misinterpreted as advice for people to apply such "techniques" to ENUM
answers provided on the Internet.
* The number of queries in a valid chain is limited; there simply aren't that
many queries that need to be made for communications-related data.
"Communications" may involve more than just application server addresses, but
it IS limited.
The new version of the ENUM standard has recommended "loop control" (see
draft-ietf-enum-3761bis-09.txt, ends of sections 5.1 and 5.2),
and has a recommended mechanism for "leakage control" (ibid, 22.214.171.124).
Thus the concerns over long chains and leakage raised in the IAB-applications
draft seem outdated, at least as far as ENUM is concerned.
Maybe it's just me, but I want a good guidelines document (so we don't HAVE to
work so hard for an ENUM-specific set :),
but I'd like the guidance to spell out answers to the six questions above, or
cover them more clearly.
At present I'm just guessing.
all the best,
On 21 Oct 2010, at 05:11, Peterson, Jon wrote:
As tempting as it is to join the cries of "imminent death of the PSTN
predicted," I wanted to drill down at some length into Ray's question on
send-n and some of Rich's comments.
Regarding send-n, the argument made by the dns-applications draft today is
that the synchronization required to coordinate different levels in the DNS
tree with the state of resources in the telephone network creates a
fundamental brittleness in this architecture. It is presented in those terms
to try to abstract out the architecture principle rather than staying
strictly within the particulars of the send-n proposal, since the guidance on
that subject did seem generalizable to proposals other than send-n. It is not
intended to be a sole and decisive refutation of the send-n proposal.
Certainly we don't want to "just say no" to the overlap dialing problem
space, but it does hope to encourage thinking about alternate ways of
satisfying the send-n requirements that don't suffer from this problem. When
importing this overlap dialing from the PSTN to the Internet, we have a
number of architectural alternatives we can explore to mirror this
functionality which may or may not map
directly onto the processes of the PSTN. It is, as the dns-applications draft
says, unclear why DNS is necessarily the best of them.
I agree that the distributed and hierarchical nature of the DNS makes it
potentially applicable to overlap dialing, since it does allow you to
traverse a tree which can ultimately delegate to the entity that sets the
length of a telephone number. What you don't mention here, however, is that
there are a number of fundamentally different approaches to overlap dialing.
Many native VoIP handsets, much like mobile phones, do not provide a "dial
tone" experience but instead wait for a user to press a "send" or "call"
button before attempting to reach a number. For those entities that do get
numbers piecemeal (like ATAs, or VoIP gateways receiving a possibly
incomplete IAM from the PSTN), I understand some implementations have a
collection timer that waits until the stream of digits has concluded before
attempting to reach a number.
However, if we assume that the delay incurred by that timer is intolerable,
we're then left with the problem that these ATA-like VoIP endpoint won't know
that an address is complete until they've tried to place a call or sent an
ENUM query that may fail. An ATA that supports ENUM might therefore make
several queries, some which will be unsuccessful, before it collects all the
digits and makes a query that returns a useful response. The motivation of
send-n is to reduce the number of those ENUM queries. It proposes an
optimization, and one that is scoped to a particular segment of the PSTN that
supports overlap dialing, and furthermore to those use cases like dial-tone
simulation or certain gatewaying architectures where timers or "send" buttons
don't address the problems. In those cases, it prevents DNS servers from
enduring the load of some of these futile queries by piggybacking onto
preliminary ENUM responses a minimum number or digits that must be collected
hing a query. As an optimization, that reduction in queries has a certain
architectural value, but we do need to assess that value objectively - I'd say
it is a bit much to construe skipping those queries in those cases as an
"essential function in the transition from analog POTS to SIP based
communication." Supporting overlap is essential - optimization is nice.
If we grant that this problem of futile queries is onerous enough to require
optimization, the question then becomes whether the optimal way for one of
these endpoints to learn the minimum number of digits is by asking the DNS a
la ENUM, in real-time as the endpoint is setting up a call. Is there a way
endpoints could acquire a picture of the numbering plan not in real-time
during call set-up, but through some prior procedure like periodically
querying for (or subscribing to) a picture of the dialing plan when the
endpoint is idle; i.e. If it is possible to reduce even further the number of
queries that need to be made in real-time while an endpoint is setting up a
call? What about endpoints that don't use ENUM - would they also care about
that minimum number of digits (say, when an endpoint just dumps a call to a
PSTN gateway for want of ENUM), and if so would it make sense to make this
information available outside of ENUM? And finally, is the stated
a good fit for the DNS? How do entities that have been delegated numbers get
the permission to provision records (for "partial" numbers) outside of their
zone of authority? Do the records require synthesis? What happens when you try
to resolve a partial number that might in fact be a prefix for blocks of
numbers in distinct administrative domains? Are there any analogous cases like
this for ordinary domain name resolution (maybe Google autocomplete will be the
overlap dialing of the future...)?
I wouldn't say that the message of the dns-applications draft is "do not
charter E2MD," in so far as it does not reject the problem space. It does try
to capture arguments that had previously only been presented anecdotally, and
it moreover intends in the future to capture the ongoing discussions we've
now begun about these subjects. I do however maintain that the previous E2MD
chater is a collection of problems that have different underlying
requirements, and that bringing them under a common architectural umbrella
may obscure their individual problem spaces rather than illuminating them.
Also, the insistence of the charter on DNS-based solutions, as opposed to
solutions that might not involve the DNS, seemed unnecessarily confining, for
send-n and other mechanisms under consideration.
On 10/20/10 3:25 PM, "Richard Shockey" <richard(_at_)shockey(_dot_)us> wrote:
And finally, regarding:
"It is unclear why this data is better maintained by the DNS
than in an unrelated application protocol."
If a device is performing an ENUM dip hoping to find a contactable SIP URI,
it is simply most efficient for the ENUM response to directly include the
Send-N metadata when needed rather than have separate queries using a
different network protocol. Also, the hierarchical and distributed nature
of the DNS protocol makes it an _ideal_ structural fit for this meta data.
I believe the onus should be on your draft to explicitly identify valid
technical reasons why the DNS protocol should _not_ be used, rather than
make vague hand-waving assertions which appear to have little or no
RS> Precisely, What is unclear is why the IETF and the IAB is suddenly
trying to block a perfectly legitimate extension of RFC 3761 that is in
various forms of global deployment, proven to work, scale and more
importantly provides a valuable and essential function in the transition
from analog POTS to SIP based communication.
Just saying no is not a solution to the real issues of number translation in
Ok a lot of people hate phone numbers including, it seems, 50% of RAI
directorate but they are not going away anytime soon.
So just say it .. is this the message? Don't even try to charter E2MD?
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